Piezoelectric/electrostrictive device and method of manufacturing same

ABSTRACT

A piezoelectric/electrostrictive device includes a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section. Piezoelectric/electrostrictive elements are arranged on at least one thin plate section of the pair of thin plate sections. A hole is formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section. The piezoelectric/electrostrictive device has a mechanism for restricting amplitude of the thin plate sections. The mechanism includes a cavity portion formed in the inner wall of the movable section and a stopper member provided on the inner wall of the fixing section, wherein the forward end of the stopper member extends into the cavity portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric/electrostrictive devicethat is provided with a movable section to be operated on the basis of adisplacement action of a piezoelectric/electrostrictive element, or apiezoelectric/electrostrictive device that is capable of detectingdisplacement of a movable section by the aid of apiezoelectric/electrostrictive element, and a method for producing thesame. In particular, the invention relates to apiezoelectric/electrostrictive device that is excellent in strength,shock resistance, and moisture resistance and that makes it possible toefficiently operate a movable section to a great extent, and a methodfor producing the same.

2. Background of the Invention

Recently, a displacement element, which makes it possible to adjust theoptical path length and the position in an order of submicron, isdemanded, for example, in the fields of optics, magnetic recording, andprecision machining. Development is advanced for the displacementelement based on the use of the displacement brought about by theinverse piezoelectric effect or the electrostrictive effect caused whena voltage is applied to a piezoelectric/electrostrictive material (forexample, a ferroelectric material).

As shown in FIG. 26, for example, those hitherto disclosed as such adisplacement element include a piezoelectric actuator comprising afixing section 204, a movable section 206, and a beam section 208 forsupporting the fixing and movable sections, which are formed integrallywith a hole 202 provided through a plate-shaped member 200 composed of apiezoelectric/electrostrictive material and with an electrode layer 210provided on the beam section 208 (see, for example, Japanese Laid-OpenPatent Publication No. 10-136665).

The piezoelectric actuator is operated such that when a voltage isapplied to the electrode layer 210, the beam section 208 makes expansionand contraction in a direction along a line obtained by connecting thefixing section 204 and the movable section 206 in accordance with theinverse piezoelectric effect or the electrostrictive effect. Therefore,the movable section 206 can perform circular arc-shaped displacement orrotational displacement in the plane of the plate-shaped member 200.

On the other hand, Japanese Laid-Open Patent Publication No. 63-64640discloses a technique in relation to an actuator based on the use of abimorph. In this technique, the electrodes of the bimorph actuator areprovided in a divided manner. The actuator is driven by selecting thedivided electrodes, and thus highly accurate positioning is performed ata high speed. JP '640 discloses a structure (especially in FIG. 4) inwhich, for example, two opposed bimorphs are used.

However, the piezoelectric actuator described above involves a problemthat the amount of operation of the movable section 206 is small,because the displacement in the direction of extension and contractionof the piezoelectric/electrostrictive material (i.e., in the in-planedirection of the plate-shaped member 200) is transmitted to the movablesection 206 as it is.

Since all the parts of the piezoelectric actuator are made ofpiezoelectric/electrostrictive materials, which are fragile materialshaving a relatively heavy weight, the mechanical strength is low, andthe piezoelectric actuator is inferior in handling performance, shockresistance, and moisture resistance. Furthermore, the piezoelectricactuator itself is heavy, and its operation tends to be affected byharmful vibrations (for example, residual vibration and noise vibrationduring high speed operation).

Then, a method may be proposed which increases the strength and theresonant frequency by thickening a beam portion, for example, in orderto improve stiffness. However, displacement and a response speed aresignificantly deteriorated due to the improvement of stiffness.

Further, the following structure is disclosed in FIG. 4 in JapaneseLaid-Open Patent Publication No. 63-64640, a joined form exists betweena mediating member and a bimorph and between a head and the bimorph(i.e., so-called piezoelectric operating sections, both of which causethe strain). In other words, the bimorph is formed contiuously rangingfrom the mediating member to the head.

As a result, when the bimorph is operated, the displacement action,which is effected with the supporting point of the joined portionbetween the mediating member and the bimorph, mutually interferes withthe displacement action which is effected with the supporting point ofthe joined point between the head and the bimorph. The expression of thedisplacement is inhibited. In this structure, it is impossible to obtaina function that the head is greatly displaced with respect to theexternal space.

The conventional device of this type has a structure which is weakagainst external forces in many situations. A problem arises in that itis difficult to handle the device and to achieve the realization of ahigh resonance frequency.

SUMMARY OF THE INVENTION

The present invention has been made taking the foregoing problems intoconsideration, and an object thereof is to provide apiezoelectric/electrostrictive device and a method for manufacturing thesame. According to the piezoelectric/electrostrictive device of thepresent invention, it is possible to obtain a displacement element thatis easy in handling, high in shock resistance against external forceswithout deteriorating the device characteristics such as thedisplacement characteristic and the response characteristic, andscarcely affected by harmful vibration, and that is capable of largedisplacement and high speed response with high mechanical strength whilebeing excellent in moisture resistance, as well as a sensor element thatmakes it possible to accurately detect vibration of the movable section.

Further, an object of the present invention is to provide apiezoelectric/electrostrictive device and a method for manufacturing thesame which can suppress occurrence of problems caused by unnecessaryvibrations during its manufacture and improve the productivity ofmanufacturing the piezoelectric/electrostrictive device.

According to the present invention, a piezoelectric/electrostrictivedevice has a pair of mutually opposing thin plate sections, a movablesection, and a fixing section for supporting the thin plate sections andthe movable section, the piezoelectric/electrostrictive deviceincludes:one or more piezoelectric/electrostrictive elements arranged onat least one thin plate section of the pair of thin plate sections, and

a hole is formed by both inner walls of the pair of thin plate sections,an inner wall of the movable section, and an inner wall of the fixingsection.

A mechanism is provided for restricting amplitude of the thin platesections. Thus, when the external force is applied to the thin platesection and the movable section, which causes their large vibration(amplitude), the mechanism can restrict the vibration (amplitude) of thethin plate section. As a result, it can prevent the thin plate sectionfrom being damaged. In this case, the thin plate section does not needto be thickened. Therefore, material characteristics of thepiezoelectric/electrostrictive element provided on the thin platesection are not deteriorated, which does not correspondingly deterioratedevice characteristics such as the displacement characteristic and theresponse characteristic.

In other words, the present invention can provide a displacement elementthat is easy in handling, high in shock resistance against the externalforce without deteriorating the device characteristics such as thedisplacement characteristic and the response characteristic, and isscarcely affected by harmful vibration, and that is capable of a largedisplacement and high speed response with high mechanical strength whilebeing excellent in moisture resistance, as well as a sensor element thatmakes it possible to accurately detect vibration of the movable section.

Further, when unnecessary vibration is applied during production, themechanism can restrict the vibration (amplitude) of the thin platesection. Therefore, damage to the thin plate section due to theunnecessary vibration can be prevented effectively, which can improvethe productivity of manufacturing the piezoelectric/electrostrictivedevice.

The mechanism may have a cavity portion formed on the inner wall of themovable section and a stopper member provided on the inner wall of thefixing section having a forward end extending into the cavity portion.Alternatively, the mechanism may have a cavity portion formed on theinner wall of the fixing section and a stopper member provided on theinner wall of the movable section having a forward end extended into thecavity portion. In this case, when the forward end of the stopper memberhits the cavity portion, vibration (amplitude) of the thin plate sectionis restricted thereby. Further, the appropriately adjusted length andthickness of the stopper member gives resilience to the stopper memberso as to absorb shocks caused when the stopper member hits the cavityportion.

Preferably, a shortest distance from the forward end of the stoppermember to an inner wall of the cavity portion in a direction ofdisplacing the movable section is not more than a tolerance limit ofamplitude of the thin plate sections. In this case, damages of the thinplate section can be prevented effectively since vibration (amplitude)of the thin plate section is not more than a tolerance limit.

The mechanism may have two buffer members formed on the inner wall ofthe fixing section and a stopper member provided on the inner wall ofthe movable section, whose forward end enters between the two buffermembers. Alternatively, the mechanism may have two buffer members formedon the inner wall of the movable section and a stopper member providedon the inner wall of the fixing section, whose forward end entersbetween the two buffer members.

In this case, when the forward end of the stopper member hits the buffermember, vibration (amplitude) of the thin plate section is restrictedthereby. Further, the appropriately adjusted aspect ratio by height andthickness of the buffer member gives resilience to the buffer member soas to absorb shocks caused when the stopper member hits the buffermember.

Furthermore, the mechanism may have a projecting portion formed fromsaid inner wall of said fixing section into said hole, wherein ashortest distance from said projecting portion to said thin platesection is not more than a tolerance limit of amplitude of said thinplate sections. In this case, damages of the thin plate section can beprevented effectively since vibration (amplitude) of the thin platesection is not more than a tolerance limit. Especially in thisarrangement, vibration (amplitude) causing a damage on the thin platesection is restricted effectively when an external force is applied tothe thin plate section directly (and intensively), which is effective inpreventing the damage on the thin plate section.

The movable section, the fixing section, the thin plate section, and themechanism can be made of ceramics or metal. That is, each of thecomponents may be made of a ceramic material, or each of them may bemade of a metal material. Alternatively, each of the components may beconstructed to have a hybrid structure obtained by combining thoseproduced from materials of ceramics and metal.

The thin plate sections, the movable section, the fixing section, andthe mechanism may comprise an integrated ceramic substrate formed bysimultaneously firing a ceramic green laminate, followed by cutting offunnecessary portions. Further, the piezoelectric/electrostrictiveelements may be of a film form and integrated with the ceramic substrateby firing.

Moreover, the piezoelectric/electrostrictive elements may have apiezoelectric/electrostrictive layer and a pair of electrodes formed onthe piezoelectric/electrostrictive layer. Thepiezoelectric/electrostrictive element may have apiezoelectric/electrostrictive layer and a pair of electrodes formed onboth sides of the piezoelectric/electrostrictive layer, and oneelectrode of the pair of electrodes may be formed on at least the thinplate section. In this arrangement, the vibration caused by thepiezoelectric/electrostrictive element can be efficiently transmittedvia the thin plate section to the movable section or the fixing section.Thus, it is possible to improve the response performance. Further, it ispreferable that the piezoelectric/electrostrictive elements areconstructed by laminating a plurality of thepiezoelectric/electrostrictive layers and the pairs of electrodes.

According to the present invention, a method is provided for producing apiezoelectric/electrostrictive device having a pair of mutually opposingthin plate sections, a movable section, and a fixing section forsupporting the thin plate sections and the movable section. Thepiezoelectric/electrostrictive device includes one or morepiezoelectric/electrostrictive elements arranged on at least one thinplate section of the pair of thin plate sections, and a hole formed byboth inner walls of the pair of thin plate sections, an inner wall ofthe movable section, and an inner wall of the fixing section. The methodcomprises the step of cutting off a predetermined portion, after formingthe piezoelectric/electrostrictive elements on at least the thin platesections, to produce the piezoelectric/electrostrictive device having amechanism for restricting amplitude of the thin plate sections.

The phrase “after forming the piezoelectric/electrostrictive element”referred to herein indicates a state in which at least thepiezoelectric/electrostrictive layer is formed on the thin platesection. As for the electrode to be formed after the formation of thepiezoelectric/electrostrictive layer, the electrode may be formed afterperforming the cutoff on a predetermined portion.

Further, according to the present invention, a method is provided forproducing a piezoelectric/electrostrictive device having a pair ofmutually opposing thin plate sections, a movable section, and a fixingsection for supporting the thin plate sections and the movable section,the piezoelectric/electrostrictive device including one or morepiezoelectric/electrostrictive elements arranged on at least one thinplate section of the pair of thin plate sections, and a hole formed byboth inner walls of the pair of thin plate sections, an inner wall ofthe movable section, and an inner wall of the fixing section. The methodcomprises the steps of producing a ceramic laminate by firing a ceramicgreen laminate containing first ceramic green sheets, second ceramicgreen sheets for constituting a mechanism for restricting amplitude ofthe thin plate sections and third ceramic green sheets for constitutingthe thin plate sections integrally, the first ceramic green sheets eachhaving a window for forming at least the hole,

forming the piezoelectric/electrostrictive elements on a part of anouter surface of the ceramic laminate for constituting the thin platesections; and

producing a piezoelectric/electrostrictive device having the mechanismfor restricting amplitude of the thin plate sections by cutting at leastonce the ceramic laminate having the piezoelectric/electrostrictiveelement.

According to the production method, it is possible to obtain adisplacement element that is scarcely affected by harmful vibration andcapable of high speed response with high mechanical strength while beingeasy in handling performance, high in shock resistance against theexternal force, and excellent in moisture resistance withoutdeteriorating the device characteristics such as the displacementcharacteristic and the response characteristic, as well as a sensorelement that makes it possible to accurately detect vibration of themovable section.

In the production methods, the exposure of the hole can be alsoperformed in the cutting step by cutting the ceramic laminate. In thiscase, the movable section (and/or fixing section) having opposingsurfaces, and the hole can be made simultaneously. However, the movablesection (and/or fixing section) and the hole can be made separately.

When the cut-off treatment is performed by means of machining,unnecessary vibration is applied. However, the mechanism can restrictthe vibration (amplitude) of the thin plate section. Therefore, damageson the thin plate section during the manufacturing processes due to theunnecessary vibration can be prevented effectively, which can improvethe productivity of manufacturing the piezoelectric/electrostrictivedevice.

Therefore, the piezoelectric/electrostrictive device according to thepresent invention can be utilized as the active device including, forexample, various transducers, various actuators, frequency regionfunctional parts (filters), transformers, vibrators, resonators,oscillators, and discriminators for the communication and the powergeneration, as well as the sensor element for various sensors including,for example, ultrasonic sensors, acceleration sensors, angular velocitysensors, shock sensors, and mass sensors. Especially, thepiezoelectric/electrostrictive device according to the present inventioncan be preferably utilized for various actuators to be used for themechanism for adjusting the displacement and the positioning and foradjusting the angle for various precision parts such as those of opticalinstruments and precision mechanical equipments.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a first embodiment;

FIG. 2 shows a perspective view illustrating a first modified example ofa piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 3 shows a perspective view illustrating a second modified exampleof a piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 4 shows a perspective view illustrating a third modified example ofa piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 5 shows a perspective view illustrating a fourth modified exampleof a piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 6 shows a perspective view illustrating a fifth modified example ofa piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 7 shows a perspective view illustrating a sixth modified example ofa piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 8 shows a perspective view illustrating a seventh modified exampleof a piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 9 shows a perspective view illustrating an eighth modified exampleof a piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 10 shows a perspective view illustrating a ninth modified exampleof a piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 11 shows, with partial omission, another example of theezoelectric/electrostrictive element;

FIG. 12 shows, with partial omission, still another example of thepiezoelectric/electrostrictive element;

FIG. 13 illustrates a situation in which both of thepiezoelectric/electrostrictive elements do not make the displacementaction in the piezoelectric/electrostrictive device according to thefirst embodiment;

FIG. 14A shows a waveform illustrating a voltage waveform to be appliedto one piezoelectric/electrostrictive element;

FIG. 14B shows a waveform illustrating a voltage waveform to be appliedto the other piezoelectric/electrostrictive element;

FIG. 15 illustrates a situation, in which thepiezoelectric/electrostrictive element makes the displacement action inthe piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 16A illustrates a process for laminating necessary ceramic greensheets in accordance with a production method of thepiezoelectric/electrostrictive device according to the first embodiment;

FIG. 16B illustrates a state, in which a ceramic green laminate isformed;

FIG. 17 illustrates a state in the production method, in which theceramic green laminate is fired into the ceramic laminate, and then apiezoelectric/electrostrictive element is formed on the ceramiclaminate;

FIG. 18 illustrates a state, in which the ceramic laminates is cut alongpredetermined cutting lines to provide thepiezoelectric/electrostrictive device according to the first embodiment;

FIG. 19 shows a perspective view illustrating a tenth modified exampleof a piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 20 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a second embodiment;

FIG. 21 shows a perspective view illustrating a modified example of apiezoelectric/electrostrictive device according to the secondembodiment;

FIG. 22 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a third embodiment;

FIG. 23 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a fourth embodiment;

FIG. 24 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a fifth embodiment;

FIG. 25 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a sixth embodiment;

FIG. 26 shows an arrangement of a piezoelectric/electrostrictive deviceconcerning an illustrative conventional technique.

DETAILED DESCRIPTION OF THE INVENTION

Explanation will be made below with reference to FIGS. 1 to 25 forillustrative embodiments of the piezoelectric/electrostrictive deviceand the method of producing the same according to the present invention.

It is noted that the piezoelectric/electrostrictive device resides in aconcept which includes the element for mutually converting the electricenergy and the mechanical energy by the aid of thepiezoelectric/electrostrictive element. Therefore, thepiezoelectric/electrostrictive device is most preferably used as theactive element such as various actuators and vibrators, especially asthe displacement element based on the use of the displacement broughtabout by the inverse piezoelectric effect or the electrostrictiveeffect. Additionally, the piezoelectric/electrostrictive device is alsopreferably used as the passive element such as acceleration sensorelements and shock sensor elements.

The term piezoelectric/electrostrictive means piezoelectric and/orelectrostrictive. For example, the terms piezoelectric/electrostrictivedevice and piezoelectric/electrostrictive element mean a piezoelectricand/or electrostrictive device and a piezoelectric and/orelectrostrictive element, respectively.

As shown in FIG. 1, a piezoelectric/electrostrictive device 10Aaccording to a first embodiment has a substrate 14 which has arectangular parallelepiped-shaped configuration as a whole and which hasa hole 12 provided at an approximately central portion in the major axisdirection thereof.

The substrate 14 comprises a pair of mutually opposing thin platesections 16 a and 16 b, a movable section 20, and a fixing section 22for supporting the pair of thin plate sections 16 a and 16 b and themovable section 20, and a piezoelectric/electrostrictive element 24 a isformed on at least a part of the thin plate section 16 a and apiezoelectric/electrostrictive element 24 b is formed at least on a partof the thin plate section 16 b. The surfaces of the thin plate sections16 a and 16 b where the piezoelectric/electrostrictive elements 24 a and24 b are formed are designated as the side surfaces of the thin platesections 16 a and 16 b.

Those usable as the substrate 14 include a structure comprising ceramicsor metal as a whole, and a hybrid structure obtained by combiningproducts produced with materials of ceramics and a metal.

Those applicable for the substrate 14 include, for example, a structure,in which respective parts are bonded to one another with an adhesivesuch as organic resin, glass or the like, a ceramic integrated structurewhich is obtained by firing and integrating a ceramic green laminateinto one unit, and a metal integrated structure integrated by brazing,soldering, eutectic bonding, or welding into one unit. Preferably, it isdesirable to construct the substrate 14 with a ceramic laminateintegrated into one unit by firing a ceramic green laminate.

The time-dependent change of state scarcely occurs in the integratedproduct of ceramic, because no adhesive exists at joined portionsbetween the respective parts, and therefore, the reliability of thejoined portion is high, giving a structure which is advantageous toensure the rigidity. Additionally, the integrated product of ceramic canbe produced with ease by means of laminating ceramic green sheets asdescribed later.

The piezoelectric/electrostrictive elements 24 a and 24 b are preparedas separate members as described later, and the preparedpiezoelectric/electrostrictive elements 24 a and 24 b are affixed to thesubstrate 14 with an adhesive, such as organic resin or glass, or bymeans of brazing, soldering or eutectic bonding. Alternatively, thepiezoelectric/electrostrictive elements 24 a and 24 b are directlyformed on the substrate 14 by using the film formation method not byusing the adhesion method described above.

The piezoelectric/electrostrictive device 10A includes the hole 12having, for example, a rectangular configuration, which is formed byboth inner walls of the pair of thin plate sections 16 a and 16 b, aninner wall 20 a of the movable section 20, and an inner wall 22 a of thefixing section 22. It is constructed such that the movable section 20 isdisplaced in accordance with the driving of thepiezoelectric/electrostrictive element 24 a and/or 24 b, or thedisplacement of the movable section 20 is detected by thepiezoelectric/electrostrictive element 24 a and/or 24 b.

Each of the piezoelectric/electrostrictive elements 24 a and 24 bcomprises a piezoelectric/electrostrictive layer 26, and a pair ofelectrodes 28 and 30 formed on both sides of thepiezoelectric/electrostrictive layer 26. A first electrode 28 of thepair of electrodes 28 and 30 is formed at least on each of the pair ofthin plate sections 16 a and 16 b.

In the embodiment shown in FIG. 1, respective forward ends of the firstelectrode 28 and the piezoelectric/electrostrictive layer 26constructing the piezoelectric/electrostrictive elements 24 a and 24 bare extended to the side surface of the movable section 20 so that aforward end of the second electrode 30 is located substantially at thecenter with respect to the length direction (Z-axis direction) of thethin plate sections 16 a and 16 b. A substantial driving portion 18 ofeach of the piezoelectric/electrostrictive elements 24 a and 24 b(portion at which the pair of electrodes 28 and 30 are overlapped witheach other with the piezoelectric/electrostrictive layer 26 interposedtherebetween) is continuously formed over a range from a part of theside surface of the fixing section 22 to a part of the side surface ofeach of the thin plate sections 16 a and 16 b. Thus, a displacementamount of the movable section 20 can be increased efficiently.

The piezoelectric/electrostrictive device 10A according to the firstembodiment has a mechanism 100 for restricting amplitude of the thinplate sections 16 a and 16 b and the movable section 20 as shown in FIG.1. The mechanism 100 includes a cavity portion 102 formed on the innerwall 20 a of the movable section 20 and a plate-like stopper member 104provided on the inner wall 22 a of the fixing section 22, whose forwardend 104 a enters the cavity portion 102.

In this case, as shown in FIG. 13, for example, a shortest distance Lcfrom the forward end 104 a of the stopper member 104 to an inner wall(side wall) 102 a of the cavity portion 102 in a direction of displacingthe movable section 20 is not more than a tolerance limit of amplitudeof the movable section 20 and the thin plate sections 16 a and 16 b.Thus, damages of the thin plate sections can be prevented effectivelysince vibration (amplitude) of the movable section 20 and thin platesections 16 a and 16 b is not more than a tolerance limit. Further, if ashortest distance from the forward end 104 a of the stopper member 104to the inner wall 102 a of the cavity portion 102 in a direction alongwhich the stopper member 104 extends is formed in a predetermined sizein accordance with the tolerance limit, damages of the thin platesections 16 a and 16 b caused by the external force from the Z-axisdirection can be prevented effectively.

The voltage is applied to the pair of electrodes 28 and 30 via terminals(pads) 32 and 34 of the respective electrodes 28 and 30 formed on bothside surfaces (element formation surfaces) of the fixing section 22,respectively. The respective terminals 32 and 34 are positioned in sucha manner that the terminal 32 corresponding to the first electrode 28 isformed at the position deviated toward the rearward end of the fixingsection 22, and the terminal 34 corresponding to the second electrode 30disposed on the side of the external space is formed at the positiondeviated toward the inner wall 22 a of the fixing section 22.

In this case, the piezoelectric/electrostrictive device 10A can beindividually fixed by utilizing the surfaces, on which the terminals 32and 34 are not arranged, and as a result, it is possible to obtain thehigh reliability for both of the fixing of thepiezoelectric/electrostrictive device 10A and the electric connectionbetween the circuit and the terminals 32 and 34. In this arrangement,the electric connection between the circuit and the terminals 32 and 34is made, for example, by means of the flexible printed circuit (alsoreferred to as FPC), the flexible flat cable (also referred to as FFC),and the wire bonding.

Structures other than the structure shown in FIG. 1 are available forthe piezoelectric/electrostrictive elements 24 a and 24 b. That is, in apiezoelectric/electrostrictive device 10Aa according to a first modifiedexample shown in FIG. 2, it is also preferable that the respectiveforward ends of the pair of electrodes 28 and 30 andpiezoelectric/electrostrictive layer 26 are substantially aligned. Asubstantial driving portion 18 of each of thepiezoelectric/electrostrictive elements 24 a and 24 b (portion at whichthe pair of electrodes 28 and 30 are overlapped with each other with thepiezoelectric/electrostrictive layer 26 interposed therebetween) iscontinuously formed over a range from a part of the side surface of thefixing section 22 to a part of the side surface of the movable section20.

Further, in the piezoelectric/electrostrictive device 10Ab according toa second modified example shown in FIG. 3, it is preferable thatrespective forward end surfaces of the pair of electrodes 28 and 30 andthe piezoelectric/electrostrictive layer 26 are substantially aligned,and a substantial driving portion 18 of each of thepiezoelectric/electrostrictive elements 24 a and 24 b is continuouslyformed over a range from a part of the outer circumferential surface ofthe fixing section 22 to a part of the side surface of each of the thinplate sections 16 a and 16 b. Alternatively, as in thepiezoelectric/electrostrictive device 10Ac according to a third modifiedexample shown in FIG. 4, it is also preferable that the respectiveforward ends of the first and second electrodes 28 and 30 constructingthe piezoelectric/electrostrictive elements 24 a and 24 b are aligned,and only the forward end of the piezoelectric/electrostrictive layer 26is projected toward the movable section 20. In the case of the structurehaving the arrangement of the piezoelectric/electrostrictive elements 24a and 24 b as shown in FIGS. 3 and 4, in the same way as in the exampleshown in FIG. 1, the movable section 20 can be displaced greatly inparallel with the fixing section 22.

Especially, in a piezoelectric/electrostrictive device 10Ac according tothe third modified example shown in FIG. 4, the movable section 20 isprovided with mutually opposing end surfaces 36 a and 36 b.

In this arrangement, because the internal residual stress generated inthe piezoelectric/electrostrictive elements 24 a and 24 b and/or thethin plate sections 16 a and 16 b at the time of manufacturing processcan be released by the movement of the end surfaces 36 a and 36 b, thedisplacement operation of the movable section 20 is not inhibited by theinternal residual stress, and it is possible to achieve the displacementoperation of the movable section 20 substantially as designed.Additionally, the release of the stress improves the mechanical strengthof the piezoelectric/electrostrictive device 10Ac.

Between the end surfaces 36 a and 36 b, a gap (air) 38 may intervene asshown in FIG. 4, or in alternative, a material different from theconstitutional material of the movable section 20, such as a resin, maybe interposed between the end surfaces. While the foregoing examplewhere the end surfaces 36 a and 36 b mutually opposing one another areprovided in the movable section 20 is described, the end surfaces 36 aand 36 b may be formed in the fixing section 22 as thepiezoelectric/electrostrictive device 10Ad according to the fourthmodified example shown in FIG. 5. Also in the arrangement of thepiezoelectric/electrostrictive elements 24 a and 24 b shown in FIG. 5,the movable section 20 can be displaced greatly in parallel with thefixing section 22.

While each of the piezoelectric/electrostrictive elements 24 a and 24 bis constituted with the piezoelectric/electrostrictive layer 26 of aone-layer structure and the pair of electrodes 28 and 30 in theforegoing examples, it is also preferred that each of thepiezoelectric/electrostrictive elements 24 a and 24 b is constituted bylaminating a plurality of the piezoelectric/electrostrictive layers 26and pairs of electrodes 28 and 30.

For example, in the piezoelectric/electrostrictive device 10Ae accordingto the fifth modified example shown in FIG. 6, thepiezoelectric/electrostrictive layers 26 and pairs of electrodes 28 and30 forms a multi-layer structure, in which the first electrodes 28 andthe second electrodes 30 are alternately stacked with one other toprovide the piezoelectric/electrostrictive elements 24 a and 24 b eachhaving a multiple stage structure at a portion (substantial drivingportion 18) at which the first electrodes 28 and the second electrodes30 are overlapped with each other with thepiezoelectric/electrostrictive layer 26 interposed therebetween. In FIG.6, the piezoelectric/electrostrictive layer 26 has a three-layerstructure, in which the first electrode 28 is formed separately on thelower surface of the first layer (side surface of the thin plate section16 a or 16 b) and the upper surface of the second layer, and the secondelectrode 30 is formed separately on the upper surface of the firstlayer and the upper surface of the third layer. Furthermore, theterminals 32 a and 32 b are formed at the both ends of the electrode 28,respectively, and the terminals 34 a and 34 b are formed at both ends ofthe second electrode 30, respectively.

In the piezoelectric/electrostrictive device 10Af according to the sixthmodified example shown in FIG. 7, the piezoelectric/electrostrictivelayer 26 and pair of the electrodes 28 and 30 form a multi-layerstructure, in which the first electrode 28 and the second electrode 30are laminated alternately to have a cross section like a comb teeth,thereby to provide the piezoelectric/electrostrictive elements 24 a and24 b each having a multiple stage structure at a portion (substantialdriving portion 18) at which the first electrodes 28 and the secondelectrodes 30 are overlapped with each other with thepiezoelectric/electrostrictive layer 26 interposed therebetween. In FIG.7, the piezoelectric/electrostrictive layer 26 has a three-layerstructure. The first electrode 28 has a cross section like a comb teeth,such that the first electrode 28 is positioned on the lower surface ofthe first layer (side surface of the thin plate section 16 a or 16 b)and the upper surface of the second layer, and the second electrode 30has a cross section like a comb teeth, such that the second electrode 30is positioned on the upper surface of the first layer and the uppersurface of the third layer. In this arrangement, the first electrodes 28are connected to one other to be used commonly, and the secondelectrodes 30 are connected to one other to be used commonly, so as todecrease the numbers of the terminals 32 and 34 in comparison to thearrangement of FIG. 6. With the multi-layer structure of thepiezoelectric/electrostrictive elements 24 a and 24 b, the increase insize can be suppressed.

In FIG. 6, a signal of the same potential can be applied to the firstelectrodes 28 and the second electrodes 30, respectively. Further,independent signals can be applied to all the electrodes 28 and 30. Inthe latter case, different amount of distortion can be formed inrespective piezoelectric/electrostrictive layers 26 to make it possibleto conduct more precise displacement control.

In the piezoelectric/electrostrictive device 10Ag according to theseventh modified example shown in FIG. 8, thepiezoelectric/electrostrictive elements 24 a and 24 b are formed in sucha manner that the forward ends thereof stay on the thin plate sections16 a and 16 b. The example in FIG. 8 illustrates that the forward endsof the piezoelectric/electrostrictive elements 24 a and 24 b arepositioned at the substantially central part with respect to thelongitudinal direction of the thin plate sections 16 a and 16 b. In thisarrangement, the movable section 20 can be advantageously subjected tolarge displacement substantially in parallel to the fixing section 22.

In the piezoelectric/electrostrictive device 10Ah according to theeighth modified example shown in FIG. 9, twopiezoelectric/electrostrictive elements 24 a 1 and 24 b 1 each having amulti-step structure are formed over the fixing section 22 and the thinplate sections 16 a and 16 b, respectively, and other twopiezoelectric/electrostrictive elements 24 a 2 and 24 b 2 each havingthe multi-step structure are formed over the movable section 20 and thethin plate sections 16 a and 16 b, respectively. This arrangement ispreferred since the movable section 20 can be subjected to remarkablylarge displacement, and the device is excellent in high speed responseby the effect of making the piezoelectric/electrostrictive elements 24 aand 24 b to have the multiple stage structure and the effect ofincreasing the sites of action to displace the movable section 20.

According to the piezoelectric/electrostrictive device 10Ai of the ninthmodified example, as shown in FIG. 10, thepiezoelectric/electrostrictive elements 24 a and 24 b are constructedsuch that the piezoelectric/electrostrictive layers 26 constitute atwo-layer structure, and the electrodes 28 are configured like combteeth. The electrode 28 is positioned on each of the lower surface ofthe first layer (side surface of the thin plate section 16 a or 16 b)and the upper surface of the second layer, with the second electrode 30being formed on the upper surface of the first layer.

With the multiple stage structure of the piezoelectric/electrostrictiveelements 24 a and 24 b, the force generated by thepiezoelectric/electrostrictive elements 24 a and 24 b is increased torealize large displacement. Further, thanks to the increased rigidity ofthe piezoelectric/electrostrictive device 10Ai, the resonance frequencyis increased, with the result that the high speed displacement operationcan be easily realized.

The term frequency herein means the frequency of the voltage wave formwhen the voltage applied to the pair of electrodes 28 and 30 is changedalternately to make horizontal displacement of the movable section 20from side to side, and the term resonance frequency herein means themaximum frequency where the movable section 20 can follow in thepredetermined vibration mode.

Though more driving force can be obtained by increasing the number ofsteps, the electric power consumption also increases accordingly.Therefore, in an actual application, the number of the stages may beappropriately determined depending on the application and the conditionin use. Furthermore, in the piezoelectric/electrostrictive devices 10Aeto 10Ai according to the fifth to ninth modified examples, even thoughthe piezoelectric/electrostrictive elements 24 a and 24 b have themultiple stage structure, the width (length in the Y axis direction) ofthe thin plate sections 16 a and 16 b is not changed. Therefore, thedevice is suitable for an actuator used for positioning and the ringingcontrol of magnetic head of a hard disk drive in an extremely narrowspace, for example.

While the above described examples of the piezoelectric/electrostrictiveelements 24 a and 24 b are constituted by the so-called sandwichstructure where the piezoelectric/electrostrictive layer 26 isinterposed between the pair of electrodes 28 and 30, the pair ofelectrodes 28 and 30 having a comb form may be formed on one majorsurface of the piezoelectric/electrostrictive layer 26 formed on theside surfaces of the thin plate sections 16 a and 16 b as shown in FIG.11. Alternatively, the pair of the electrodes 28 and 30 having a combform may be embedded in the piezoelectric/electrostrictive layer 26 onthe side surfaces of the thin plate sections 16 a and 16 b as shown inFIG. 12.

In the case of the structure shown in FIG. 11, there is an advantage inthat the electric power consumption can be suppressed to small, and inthe case of the structure shown in FIG. 12, the inverse piezoelectriceffect or the electrostrictive effect in the direction of the electricfield that has large generating force and distortion can be effectivelyutilized, and therefore it is advantageous to generate largedisplacement.

Specifically, the piezoelectric/electrostrictive elements 24 a and 24 bshown in FIG. 11 comprise the pair of electrodes 28 and 30 having thecomb structure formed on one major surface of thepiezoelectric/electrostrictive layer 26, and have such a structure thatthe first electrode 28 and the second electrode 30 mutually oppose oneanother with a gap 29 having a constant width. While an example wherethe pair of electrodes 28 and 30 are formed on one major surface of thepiezoelectric/electrostrictive layer 26 is shown in FIG. 11, the pair ofelectrodes 28 and 30 may be formed between the thin plate sections 16 aand 16 b and the piezoelectric/electrostrictive layer 26, or inalternative, the pair of electrodes 28 and 30 having the comb form isrespectively formed on the major surface of thepiezoelectric/electrostrictive layer 26 and between the thin platesections 16 a and 16 b and the piezoelectric/electrostrictive layer 26.

On the other hand, the piezoelectric/electrostrictive elements 24 a and24 b shown in FIG. 12 comprise the pair of electrodes 28 and 30 havingthe comb form buried in the piezoelectric/electrostrictive layer 26, andhave such a structure that the first electrode 28 and the secondelectrode 30 mutually oppose one another with a gap 29 having a constantwidth.

The piezoelectric/electrostrictive elements 24 a and 24 b shown in FIG.11 and FIG. 12 can also be suitably used in thepiezoelectric/electrostrictive device 10A according to the firstembodiment and the like. In the case where the pair of electrodes 28 and30 having the comb form as in the piezoelectric/electrostrictiveelements 24 a and 24 b as shown in FIG. 11 and FIG. 12, the displacementof the piezoelectric/electrostrictive elements 24 a and 24 b can beincreased by reducing the pitch D of the comb teeth of the respectiveelectrodes 28 and 30.

The operation of the piezoelectric/electrostrictive device 10A accordingto the first embodiment will be described below. In the case where thetwo piezoelectric/electrostrictive elements 24 a and 24 b are in thenatural state, i.e., both the piezoelectric/electrostrictive elements 24a and 24 b do not conduct displacement operation, the major axis m ofthe piezoelectric/electrostrictive device 10A (major axis of the fixingsection) is substantially coaxially aligned with the central axis n ofthe movable section 20 as shown in FIG. 13.

From that state, a sine wave Wa having a predetermined bias voltage Vbis applied to the pair of electrodes 28 and 30 of onepiezoelectric/electrostrictive element 24 a as shown in FIG. 14A, and asine wave Wb having a phase that is different from the sine wave Wa byabout 180° is applied to the pair of electrodes 28 and 30 of the otherpiezoelectric/electrostrictive element 24 b as shown in FIG. 14B.

At the step where the maximum voltage is applied to the pair ofelectrodes 28 and 30 of one piezoelectric/electrostrictive element 24 a,the piezoelectric/electrostrictive layer 26 of the onepiezoelectric/electrostrictive element 24 a suffers contractivedisplacement in the major surface direction. Accordingly, as shown inFIG. 15, a stress in such a direction that bends the thin plate section16 a, for example, in the right direction as shown by the arrow A isapplied to the thin plate section 16 a, and thus the thin plate section16 a is bent in the right direction. At this time, the pair ofelectrodes 28 and 30 of the other piezoelectric/electrostrictive element24 b is in the state where no voltage is applied thereto, and the otherthin plate section 16 b is bent in the right direction following thebending of the thin plate section 16 a.

As a result, the movable section 20 is displaced, for example, in theright direction with respect to the major axis m of thepiezoelectric/electrostrictive device 10A. The displacement amountvaries depending on the maximum value of the voltage applied to therespective piezoelectric/electrostrictive elements 24 a and 24 b, andfor example, when the maximum value is increased, the displacementamount is also increased.

In this embodiment, when the movable section 20 is displaced, a forwardend 104 a of a stopper member 104 is arranged to hit a side wall 102 aof a cavity portion 102 provided on an inner wall 20 a of the movablesection 20 to suppress the displacement of the movable section 20. Thus,when the external force or the like is applied to the movable section20, which causes its large vibration (amplitude), the action of themechanism 100 (the forward end 104 a of the stopper member 104 hits theside wall 102 a of the cavity portion 102) can restrict the vibration(amplitude) of the movable section 20. As a result, it can prevent thethin plate sections 16 a and 16 b from being damaged. In this case, thethin plate sections 16 a and 16 b not need to be thickened forpreventing such damages. Therefore, material characteristics of thepiezoelectric/electrostrictive elements 24 a and 24 b provided on thethin plate sections 16 a and 16 b are not deteriorated, which does notdeteriorate device characteristics such as the displacementcharacteristic and the response characteristic.

Particularly, in the case where a piezoelectric/electrostrictivematerial having a coercive electric field is applied to the materialconstituting the piezoelectric/electrostrictive layer 26, it is possiblethat the bias voltage Vb is so adjusted that the level of the minimumvalue is a slightly negative level as shown in the two-dot chain linesin FIG. 14A and FIG. 14B. In this case, according to the drive of thepiezoelectric/electrostrictive element, to which the negative level isapplied (for example, the other piezoelectric/electrostrictive element24 b), a stress in the direction of bending of the one thin platesection 16 a is generated in the other thin plate section 16 b, wherebyit becomes possible to increase the displacement amount of the movablesection 20. That is, by using the wave form shown by the two-dot chainlines in FIG. 14A and FIG. 14B, the piezoelectric/electrostrictiveelement 24 a or 24 b, to which the negative level is applied,advantageously supports the piezoelectric/electrostrictive elements 24 aor 24 b mainly conducting the displacement operation.

In the piezoelectric/electrostrictive device 10Ah according to theeighth modified example shown in FIG. 9, the voltage shown in FIG. 14A(see the sine wave Wa) is applied, for example, to the diagonallyarranged piezoelectric/electrostrictive element 24 a 1 and thepiezoelectric/electrostrictive element 24 b 2, and the voltage shown inFIG. 14B (see the sine wave Wb) is applied to the otherpiezoelectric/electrostrictive element 24 a 2 and thepiezoelectric/electrostrictive element 24 b 1.

Therefore, in the piezoelectric/electrostrictive device 10A according tothe first embodiment and the piezoelectric/electrostrictive devices 10Aato 10Aj according to the modified examples, the minute displacement ofthe piezoelectric/electrostrictive elements 24 a and 24 b is amplifiedto large displacement operation by utilizing the bending of the thinplate sections 16 a and 16 b and is transferred to the movable section20, and thus the movable section 20 can be subjected to largedisplacement with respect to the major axis m of thepiezoelectric/electrostrictive device 10A.

Especially, the mechanism 100 is provided for restricting the amplitudeof the movable section 20 and the thin plate sections 16 a and 16 b.Thus, when the external force is applied to the movable section 20 andthe thin plate sections 16 a and 16 b, which causes their largevibration (amplitude), the mechanism 100 can restrict the vibration(amplitude) of the movable section 20 and the thin plate sections 16 aand 16 b. As a result, it can prevent the thin plate sections from beingdamaged. In this case, the thin plate sections 16 a and 16 b not need tobe thickened. Therefore, material characteristics of thepiezoelectric/electrostrictive elements 24 a and 24 b provided on thethin plate sections 16 a and 16 b are not deteriorated, which does notdeteriorate device characteristics such as the displacementcharacteristic and the response characteristic.

Accordingly, in the first embodiment, the high-speed response ispossible without deteriorating the device characteristics such as thedisplacement characteristic and the response characteristic.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, since the movable section 20, the thin plate sections 16 aand 16 b and the fixing section 22 are integrated, and all of thecomponents are not necessarily formed with the relatively heavypiezoelectric/electrostrictive material, high mechanical strength andexcellence in handling performance, shock resistance, and moistureresistance can be obtained without being subjected to the influence ofharmful vibration (for example, residual vibration and noise vibrationon high speed operation) during operation.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, the piezoelectric/electrostrictive elements 24 a and 24 bare constituted to have the piezoelectric/electrostrictive layer 26 andthe pair of electrodes 28 and 30 formed on both sides of thepiezoelectric/electrostrictive layer 26, and the first electrode 28 ofthe pair of the electrodes 28 and 30 is formed on at least the outersurface of the thin plate sections 16 a and 16 b, whereby the vibrationcaused by the piezoelectric/electrostrictive elements 24 a and 24 b canbe effectively transmitted to the movable section 20 via the thin platesections 16 a and 16 b, so as to improve the response performance.

Particularly, in the piezoelectric/electrostrictive device 10A accordingto the first embodiment, the piezoelectric/electrostrictive devices 10Abto 10Ag according to the second to seventh modified examples, and thepiezoelectric/electrostrictive device 10Ai according to the ninthmodified embodiment, the part of the piezoelectric/electrostrictivelayer 26 sandwiched by the pair of electrodes 28 and 30 (substantialdriving portion 18) is continuously formed from a part of the fixingsection 22 to a part of the thin plate sections 16 a and 16 b.

In the case where the substantial driving portion 18 is formed furtherto a part of the movable section 20, there is a possibility that thedisplacement operation of the movable section 20 is restricted by thesubstantial driving portion 18 to fail to obtain large displacement, butin this embodiment, because the substantial driving portion 18 is formednot over both the movable section 20 and the fixing section 22, thedisplacement amount of the movable section 20 can be made large.

In particular, it is preferable to employ the constitutions of thesecond, third, fourth and seventh piezoelectric/electrostrictive devices10Ab, 10Ac, 10Ad and 10Ag, since the movable section 20 can be displacedsubstantially in parallel to the fixing section 22, with the result thatthe damages on the thin plate sections 16 a and 16 b are suppressedbecause of the increase in shock resistance against the external force.

On the other hand, in the case where the piezoelectric/electrostrictiveelements 24 a and 24 b are formed on a part of the movable section 20,it is preferable that the substantial driving portion 18 is formed to bepositioned from a part of the movable section 20 to a part of the thinplate sections 16 a and 16 b. This is because when the substantialdriving portion 18 is formed further to a part of the fixing section 22,the displacement operation of the movable section 20 is restricted asdescribed in the foregoing.

In this case, when all the first electrode 28, the second electrode 30and the piezoelectric/electrostrictive layer 26 are formed to bepositioned from a part of the movable section 20 to a part of the thinplate sections 16 a and 16 b, in addition to the positional relationshipof the substantial driving portion 18, the movable section 20 can bedisplaced substantially in parallel to the fixing section 22, and thusit is preferable since the damages on the thin plate sections 16 a and16 b are suppressed and shock resistance against the external force isincreased.

A preferred constitutional embodiment of thepiezoelectric/electrostrictive device 10A according to this embodimentwill be described.

In order to ensure the displacement operation of the movable section 20,it is preferable that the length Lg where the substantial drivingportion 18 of the piezoelectric/electrostrictive elements 24 a and 24 boverlaps the fixing section 22 or the movable section 20 is ½ or more ofthe thickness Ld of the thin plate sections 16 a and 16 b.

The ratio La/Lb of the distance La between the inner walls of the thinplate sections 16 a and 16 b (distance in the X axis direction) to thewidth Lb of the thin plate sections 16 a and 16 b is from 0.5 to 20. Theratio La/Lb is preferably from 1 to 10, and more preferably from 2 to 8.The stipulated value of the ratio La/Lb is the provision based on thefinding that the displacement amount of the movable section 20 isincreased, and the displacement can be predominantly obtained in the X-Zplane.

On the other hand, the ration Le/La of the length Le of the thin platesections 16 a and 16 b (length in the Z axis direction) to the distanceLa between the inner walls of the thin plate sections 16 a and 16 b ispreferably from 0.5 to 10, and more preferably from 0.7 to 5. Thestipulated value of the ratio Le/La is the provision based on thefinding that the displacement amount of the movable section 20 isincreased, and the displacement operation can be conducted at a highresonance frequency (i.e., a high response speed can be attained).

Therefore, in order to make the piezoelectric/electrostrictive device10A according to the first embodiment to have a suppressed bendingdisplacement or vibration in the Y direction and excellence in highspeed response performance with large displacement at a relatively lowvoltage, it is preferable that the ratio La/Lb is from 0.5 to 20, andthe ratio Le/La is from 0.5 to 10, and it is more preferable that theratio La/Lb is from 1 to 10, and the ratio Le/La is from 0.7 to 5.Furthermore, it is preferable that a gel-like material, such as siliconegel, is filled in the hole 12.

The length Lf of the movable section 20 (length in the Z axis direction)is preferably short. This is because the light weight and the increasein resonance frequency can be realized by the increase thereof. However,in order to ensure the rigidity of the movable section 20 in the X axisdirection and the displacement thereof, it is preferable that the ratioLf/Ld of the length Lf of the movable section 20 (length in the Z axisdirection) to the thickness Ld of the thin plate sections 16 a and 16 bis 3 or more, and more preferably 5 or more.

The actual dimensions of the respective parts are determined byconsidering the connecting area of the movable section 20 for attachmentof the parts, the connecting area for attaching the fixing section 22 toother members, the connecting area for attaching the terminals for theelectrodes or the like, and the strength, the durability, the necessarydisplacement amount, the resonance frequency and the driving voltage ofthe entire piezoelectric/electrostrictive device 10A.

Specifically, the distance La between the inner walls of the thin platesections 16 a and 16 b is preferably from 100 μm to 2,000 μm, and morepreferably from 200 μm to 1,000 μm. The width Lb of the thin platesections 16 a and 16 b is preferably from 50 μm to 2,000 μm, and morepreferably from 100 μm to 500 μm. The relationship of the thickness Ldof the thin plate sections 16 a and 16 b to the width Lb of the thinplate sections 16 a and 16 b is Lb>Ld in order to effectively suppressthe bending displacement, which is the displacement component in the Yaxis direction, and the thickness Ld of the thin plate sections 16 a and16 b is preferably from 2 μm to 100 μm, and more preferably from 4 μm to50 μm.

The length Le of the thin plate sections 16 a and 16 b is preferablyfrom 200 to 3,000 μm, and more preferably from 300 μm to 2,000 μm. Thelength Lf of the movable section 20 is preferably from 50 μm to 2,000μm, and more preferably from 100 μm to 1,000 μm.

By employing the arrangement, such an excellent effect is exhibited thatwhile the displacement in the Y axis direction does not exceed 10% withrespect to the displacement in the X direction, the low voltage drivingcan be conducted by appropriately adjusting the dimensional ratios andthe actual dimensions within the foregoing ranges, and the displacementcomponent in the Y axis direction can be suppressed to 5% or less. Thatis, the movable section 20 is displaced substantially in one direction,i.e., the X axis direction, and excellent in high speed responseperformance and provides large displacement with a relatively lowvoltage.

In the piezoelectric/electrostrictive device 10A, the shape of thedevice is not the conventional plate form, but the movable section 20and the fixing section 22 exhibit a rectangular parallelepiped shape,and the pair of the thin plate sections 16 a and 16 b are provided insuch a manner that the side surfaces of the movable section 20 and thefixing section 22 are continued, whereby the rigidity in the Y directionof the piezoelectric/electrostrictive device 10A can be selectivelyincreased.

That is, the piezoelectric/electrostrictive device 10A can selectivelygenerate only the operation of the movable section 20 in the plane (inthe XZ plane), and the operation of the movable section 20 in the YZplane (operation in the so-called bending direction) can be suppressed.

The respective components of the piezoelectric/electrostrictive device10A according to the first embodiment will be described.

As described above, the movable section 20 is the portion which isoperated on the basis of the driving amount of the thin plate sections16 a and 16 b, and a variety of members are attached thereto dependingon the purpose of use of the piezoelectric/electrostrictive device 10A.For example, when the piezoelectric/electrostrictive device 10A is usedas a displacement element, a shield plate for an optical shutter or thelike is attached thereto, and especially, when thepiezoelectric/electrostrictive device 10A is used for the mechanism forpositioning or suppressing the ringing of a magnetic head of a hard diskdrive, a member required to be positioned is attached thereto,including, for example, the magnetic head, a slider provided with themagnetic head, and a suspension provided with the slider.

As described above, the fixing section 22 is the portion for supportingthe thin plate sections 16 a and 16 b and the movable section 20. Inaddition, the fixing section 22 also serves as the portion for attachingand securing the piezoelectric/electrostrictive device 10A to anothermember. For example, when the fixing section 22 is utilized to positionthe magnetic head of the hard disk drive, the entirepiezoelectric/electrostrictive device 10A is fixed by supporting andsecuring the fixing section 22, for example, to a carriage arm attachedto VCM (voice coil motor) or a fixing plate or a suspension attached tothe carriage arm. As shown in FIG. 1, the terminals 32 and 34 fordriving the piezoelectric/electrostrictive elements 24 a and 24 b andother members are arranged on the fixing section 22 in some cases.

The material for constructing the movable section 20 and the fixingsection 22 is not specifically limited provided that it has rigidity.However, it is possible to suitably use ceramics, to which the ceramicgreen sheet-laminating method is applicable as described later.Specifically, the material includes, for example, materials containing amajor component of zirconia represented by fully stabilized zirconia andpartially stabilized zirconia, alumina, magnesia, silicon nitride,aluminum nitride, and titanium oxide, as well as materials containing amajor component of a mixture of those materials, and in view of the highmechanical strength and the high toughness, it is preferable to use amaterial containing a major component of zirconia, especially fullystabilized zirconia and a material containing a major component ofpartially stabilized zirconia. The metallic material is not limitedprovided that it has rigidity, and the metallic material includes, forexample, stainless steel and nickel. Further, it is also possible to useengineering plastics.

As described above, the thin plate sections 16 a and 16 b are theportions, which are driven in accordance with the displacement of thepiezoelectric/electrostrictive elements 24 a and 24 b. The thin platesections 16 a and 16 b are the thin plate-shaped member havingflexibility, and they function to amplify the expansion and contractingdisplacement of the piezoelectric/electrostrictive elements 24 a and 24b arranged on the surface as the bending displacement and transmit thedisplacement to the movable section 20. Therefore, it is enough that theshape or the material of the thin plate sections 16 a and 16 b providesthe flexibility and the mechanical strength of such a degree that it isnot broken by the bending displacement. It is possible to makeappropriate selection considering the response performance and theoperability of the movable section 20.

It is preferable that the thickness Ld of the thin plate sections 16 aand 16 b is preferably about from 2 μm to 100 μm. It is preferable thatthe combined thickness of the thin plate section 16 a (or 16 b) and thepiezoelectric/electrostrictive element 24 a (or 24 b) is from 7 μm to500 μm. It is preferable that the thickness of the electrodes 28 and 30is from 0.1 to 50 μm, and the thickness of thepiezoelectric/electrostrictive layer 26 is from 3 to 300 μm. The widthLb of the thin plate sections 16 a and 16 b is preferably from 50 μm to2,000 μm.

Ceramics, which is similarly used for the movable section 20 and thefixing section 22, can be preferably used as the material forconstructing the thin plate sections 16 a and 16 b. A materialcontaining a major component of zirconia, especially fully stabilizedzirconia and a material containing a major component of partiallystabilized zirconia are most preferably used because the mechanicalstrength is large even in the case of a thin wall thickness, thetoughness is high, and the reactivity with thepiezoelectric/electrostrictive layer and the electrode material issmall.

When the thin plate sections 16 a and 16 b are made of a metallicmaterial, it is enough that the metallic material has flexibility andthe metallic material is capable of bending displacement as describedabove, and preferably, it is desirable that they are made of aniron-based material such as various stainless steel materials andvarious spring steel materials. Alternatively, it is desirable that theyare made of a non-ferrous material such as beryllium copper, phosphorbronze, nickel, and nickel-iron alloy.

Those, which are fully stabilized or partially stabilized as follows,are preferably used as fully stabilized zirconia or partially stabilizedzirconia as described above. That is, the compound to be used for fullystabilizing or partially stabilizing zirconia includes yttrium oxide,ytterbium oxide, cerium oxide, calcium oxide and magnesium oxide. Whenat least one compound of them is added and contained, zirconia ispartially or fully stabilized, and as for the stabilization, thezirconia can be stabilized not only by adding one type of the compoundbut also by adding a combination of the compounds.

The amount of addition of each of the compounds is desirably from 1 to30 molt, and preferably from 1.5 to 10 molt for yttrium oxide orytterbium oxide; from 6 to 50 mol %, and preferably from 8 to 20 mol %for cerium oxide; and from 5 to 40 mol %, and preferably from 5 to 20molt for calcium oxide or magnesium oxide, and it is preferable to useyttrium oxide as a stabilizer. In this case, the addition amount ofyttrium oxide is desirably from 1.5 to 10 mol %, and more preferablyfrom 2 to 4 mol %. For example, alumina, silica, or transition metaloxide may be added as an additive of sintering aid or the like in arange of from 0.05 to 20% by weight, and when the firing integrationbased on the film formation method is adopted as a technique for formingthe piezoelectric/electrostrictive elements 24 a and 24 b, it is alsopreferable to add, for example, alumina, magnesia, and transition metaloxide as an additive.

In order to obtain the mechanical strength and the stable crystal phase,it is desirable that the average crystal grain size of zirconia is from0.05 to 3 μm, and preferably from 0.05 to 1 μm. As described above,ceramics can be used for the thin plate sections 16 a and 16 b in thesame manner as the movable section 20 and the fixing section 22, andpreferably, it is advantageous to construct the thin plate sections 16 aand 16 b with a substantially identical material in view of thereliability of the joined portion and the strength of thepiezoelectric/electrostrictive device 10A, in order to reduce anycomplicated procedure of the production.

The piezoelectric/electrostrictive elements 24 a and 24 b have at leastthe piezoelectric/electrostrictive layer 26 and the pair of electrodes28 and 30 for applying the electric field to thepiezoelectric/electrostrictive layer 26. It is possible to use, forexample, piezoelectric/electrostrictive elements of the unimorph typeand the bimorph type, and those of the unimorph type relating to thecombination of the thin plate sections 16 a and 16 b are suitable forthe piezoelectric/electrostrictive device 10A as described above becausethey are excellent in stability of the generated displacement amount andthey are advantageous to realize the light weight.

For example, as shown in FIG. 1, it is possible to suitably use, forexample, the piezoelectric/electrostrictive element comprising the firstelectrode 28, the piezoelectric/electrostrictive layer 26, and thesecond electrode 30 which are stacked in the layered configuration, andadditionally, it is also preferable to provide the multiple stagestructure as shown in FIGS. 6 to 10.

As shown in FIG. 1, the piezoelectric/electrostrictive elements 24 a and24 b are preferably formed on the outer surface of thepiezoelectric/electrostrictive device 10A in view of the fact that thethin plate sections 16 a and 16 b can be driven to a greater extent, andthe piezoelectric/electrostrictive elements 24 a and 24 b may be formedon the inner surface of the piezoelectric/electrostrictive device 10A,i.e., on the inner wall surface of the hole 12 depending on, forexample, the form of use. Alternatively, thepiezoelectric/electrostrictive elements 24 a and 24 b may be formed bothon the outer surface and on the inner surface of thepiezoelectric/electrostrictive device 10A.

Piezoelectric ceramics is preferably used for thepiezoelectric/electrostrictive layer 26, and it is also possible to useelectrostrictive ceramics, ferroelectric ceramics, or anti-ferroelectricceramics. However, when the piezoelectric/electrostrictive device 10A isused, for example, to position the magnetic head of the hard disk drive,because it is important to provide the linearity concerning thedisplacement amount of the movable section 20 and the driving voltage orthe output voltage, it is preferable to use a material having smallstrain hysteresis, and it is also preferable to use a material having acoercive electric field of not more than 10 kV/mm.

Specifically, it is possible to use materials such as ceramicscontaining, for example, lead zirconate, lead titanate, lead magnesiumniobate, lead nickel niobate, lead zinc niobate, lead manganese niobate,lead antimony stannate, lead manganese tungstate, lead cobalt niobate,barium titanate, sodium bismuth titanate, potassium sodium niobate, andstrontium bismuth tantalate singly or in mixture.

Especially, a material containing a major component of lead zirconate,lead titanate, and lead magnesium niobate, or a material containing amajor component of sodium bismuth titanate is preferably used, in orderto obtain the product having a stable composition with a highelectromechanical coupling factor and a piezoelectric constant and withsmall reactivity with the thin plate sections (ceramics) 16 a and 16 bduring the firing of the piezoelectric/electrostrictive layer 26.

It is also preferable to use ceramics, obtained by adding to thematerial described above, for example, oxides of lanthanum, calcium,strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,manganese, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium,tantalum, lithium, bismuth, and tin singly or in mixture.

For example, when lanthanum or strontium is contained in the majorcomponents of lead zirconate, lead titanate and lead magnesium niobate,an advantage is obtained in some cases, for example, in such a way thatthe coercive electric field and the piezoelectric characteristic can beadjusted.

It is desirable to avoid the addition of a material such as silica,which tends to form glass. This is because the material such as silicatends to react with the piezoelectric/electrostrictive material duringthe heat treatment for the piezoelectric/electrostrictive layer, wherebyas a result, the composition is varied, and the piezoelectriccharacteristic is deteriorated.

On the other hand, it is preferable that the pair of electrodes 28 and30 of the piezoelectric/electrostrictive elements 24 a and 24 b are madeof metal which is solid at room temperature and which is excellent inconductivity. For example, it is possible to use metal simple substanceor alloy of, for example, aluminum, titanium, chromium, iron, cobalt,nickel, copper, zinc, niobium, molybdenum, ruthenium, palladium,rhodium, silver, tin, tantalum, tungsten, iridium, platinum, gold andlead. It is also preferable to use a cermet material obtained bydispersing, in the metal described above, the same material as that ofthe piezoelectric/electrostrictive layer 26 or the thin plate sections16 a and 16 b.

The material for the electrodes 28 and 30 of thepiezoelectric/electrostrictive elements 24 a and 24 b is selected anddetermined depending on the method of forming thepiezoelectric/electrostrictive layer 26. For example, when thepiezoelectric/electrostrictive layer 26 is formed by firing on the firstelectrode 28 after the first electrode 28 is formed on the thin platesections 16 a and 16 b, it is necessary for the first electrode 28 touse high melting point metal such as platinum, palladium, aplatinum-palladium alloy, a silver-palladium alloy and a gold-palladiumalloy which does not change at the firing temperature for thepiezoelectric/electrostrictive layer 26. However, because the electrodeformation can be performed at a low temperature for the second electrode30 which is formed on the piezoelectric/electrostrictive layer 26 afterforming the piezoelectric/electrostrictive layer 26, it is possible forthe second electrode 30 to use low melting point metal such as aluminum,gold and silver.

The thickness of the electrodes 28 and 30 also serve as a factor toconsiderably decrease the displacement of thepiezoelectric/electrostrictive elements 24 a and 24 b. Therefore, it ispreferable, especially for the electrodes 28 and 30 formed after thefiring of the piezoelectric/electrostrictive layer 26, to use organicmetal paste capable of obtaining a dense and thinner film after thefiring, for example, a material such as gold resinate paste, platinumresinate paste and silver resinate paste.

The method of producing the piezoelectric/electrostrictive device 10Aaccording to the first embodiment will be described with reference toFIGS. 16A to 18.

Ceramics is preferably used for the constitutive material for each ofthe members of the piezoelectric/electrostrictive device 10A accordingto the first embodiment of the invention. It is preferable that theconstitutive elements of the piezoelectric/electrostrictive device 10Aconcerning the substrate 14 except for thepiezoelectric/electrostrictive elements 24 a and 24 b, i.e., the thinplate sections 16 a and 16 b, the fixing section 22 and the movablesection 20 are produced by using the ceramic green sheet-laminatingmethod. On the other hand, it is preferable that thepiezoelectric/electrostrictive elements 24 a and 24 b as well as therespective terminals 32 and 34 are produced by using the film formationmethod, for example, for the thin film and the thick film.

According to the ceramic green sheet-laminating method in which therespective members of the substrate 14 of thepiezoelectric/electrostrictive device 10A can be formed integrally, thetime-dependent change of state scarcely occurs at the joined portions ofthe respective members, and therefore, this method provides the highreliability of the joined portion, and it is advantageous to ensure therigidity.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, the boundary portion (joined portion) between the thin platesections 16 a and 16 b and the fixing section 22 and the boundaryportion (joined portion) between the thin plate sections 16 a and 16 band the movable section 20 function as supporting points for expressingthe displacement. Therefore, the reliability of the joined portion is animportant point, which dominates the characteristic of thepiezoelectric/electrostrictive device 10A.

Because the production methods described below are excellent inreproducibility and formability, it is possible to obtain thepiezoelectric/electrostrictive device having a predetermined shapewithin a short period of time with good reproducibility.

A method of producing the piezoelectric/electrostrictive device 10Aaccording to the first embodiment of the invention will be specificallyexplained below. The following definitions are now made. The laminatethat is obtained by laminating the ceramic green sheets is defined to bethe ceramic green laminate 58 (see, for example, FIG. 16B). Theintegrated matter that is obtained by firing the ceramic green laminate58 is defined to be the ceramic laminate 60 (see, for example, FIG. 17).The integrated matter comprising the movable section 20, the thin platesections 16 a and 16 b, and the fixing section 22 that is obtained bycutting off unnecessary portions from the ceramic laminate 60 is definedto be the ceramic substrate 14C (see FIG. 18).

In this production method, the ceramic laminate 60 is finally cut intochip units to produce a large number of piezoelectric/electrostrictivedevices 10A. However, in order to simplify the explanation, descriptionwill be made principally for the case in which one individual ofpiezoelectric/electrostrictive device 10A is produced.

At first, for example, a binder, a solvent, a dispersing agent and aplasticizer are added and mixed with a ceramic powder such as zirconiato prepare a slurry. The slurry is subjected to a degassing treatment,and then a ceramic green sheet having a predetermined thickness isprepared in accordance with, for example, the reverse roll coater methodand the doctor blade method.

Subsequently, the ceramic green sheet is processed into those havingvarious shapes as shown in FIG. 16A in accordance with, for example, thepunching out based on the die and the laser machining to obtain aplurality of ceramic green sheets 50A, 50B, 52A, 52B, 54A, 54B and 56for forming the substrate.

The ceramic green sheets 50A, 50B, 52A, 52B, 54A, 54B and 56 include theplurality of ceramic green sheets 50A and 50B each of which is formedwith at least a window 10 for forming the hole 12 thereafter, theplurality of ceramic green sheets 54A and 54B each of which iscontinuously formed with at least a window 110 for forming the hole 12thereafter and at least a window 112 for forming a cavity portion 102,one, for example, ceramic green sheet 56 which is formed with at least awindow 114 to be formed into a stopper member 122 thereafter, and aplurality of ceramic green sheets 52A, 52B to be formed into the thinplate sections 16 a and 16 b thereafter. The numbers of ceramic greensheets referred to above are discussed by way of example only.

Thereafter, as shown in FIG. 16B, the ceramic green sheets 50A, 50B,52A, 52B, 54A, 54B and 56 are laminated and pressure-secured so that theceramic green sheets 50A, 50B, 54A, 54B and 56 are interposed betweenthe ceramic green sheets 52A, 52B and the ceramic green sheet 56 islocated at the center with the ceramic green sheets 54A and 54B on itstop and bottom, respectively, to form a ceramic green laminate 58. Then,the ceramic green laminate 58 is fired to obtain a ceramic laminate 60(see FIG. 17).

There is no limitation for the number of pressure-securing steps and thesequence for the purpose of the laminating and integration into oneunit. These factors can be appropriately determined depending on thestructure, for example, so that the desired structure is obtained on thebasis of, for example, the shape of the windows 110, 112 and 114 and thenumber of ceramic green sheets.

It is unnecessary that the shape of the windows 110, 112 and 114 isidentical in all cases, and it can be determined depending on thedesired function. There is also no limitation for the number of ceramicgreen sheets and the thickness of each of the ceramic green sheets.

In the pressure-securing step, it is possible to further improve thelaminating performance by applying the heat. The laminating performanceat the boundary of the ceramic green sheet can be improved by providingan auxiliary joining layer, for example, by applying and printing, ontothe ceramic green sheet, a paste or a slurry principally containing aceramic powder (it is preferable to use a composition which is the sameas or similar to that of the ceramics used for the ceramic green sheetin order to ensure the reliability) and the binder. When the ceramicgreen sheets 52A and 52B are thin, it is preferable to handle them witha plastic film, especially with a polyethylene terephthalate film coatedwith a releasing agent based on silicone on the surface.

Subsequently, as shown in FIG. 17, the piezoelectric/electrostrictiveelements 24 a and 24 b are formed respectively on both surfaces of theceramic laminate 60, i.e., on the surfaces corresponding to thesurfaces, at which the ceramic green sheets 52A and 52B are laminated.Those usable as the method of forming the piezoelectric/electrostrictiveelements 24 a and 24 b include the thick film formation method, such asthe screen printing method, the dipping method, the coating method andthe electrophoresis method, and the thin film formation method, such asthe ion beam method, the sputtering method, the vacuum vapor deposition,the ion plating method, the chemical vapor deposition method (CVD) andthe plating.

When the piezoelectric/electrostrictive elements 24 a and 24 b areformed by using the film formation method as described above, thepiezoelectric/electrostrictive elements 24 a and 24 b and the thin platesections 16 a and 16 b can be integrally joined and arranged withoutusing any adhesive, whereby it is possible to ensure the reliability andthe reproducibility, and it is easy to form the stack.

In this case, it is preferable that the piezoelectric/electrostrictiveelements 24 a and 24 b are formed by means of the thick film formationmethod. This is because, especially, when thepiezoelectric/electrostrictive layer 26 is formed by using the thickfilm formation method, the film can be formed by using, for example, apaste, a slurry, a suspension, an emulsion, or a sol containing a majorcomponent of particles or powder of piezoelectric ceramics having anaverage particle size of from 0.01 to 5 μm, preferably from 0.05 to 3μm, and thus it is possible to obtain goodpiezoelectric/electrostrictive characteristics by firing the formedfilm.

The electrophoresis method is advantageous in that the film can beformed at a high density with a high shape accuracy. The screen printingmethod is advantageous to simplify the production step because it ispossible to simultaneously perform the film formation and the patternformation.

The formation of the piezoelectric/electrostrictive elements 24 a and 24b will be described. At first, the ceramic green laminate 58 is firedand integrated into one unit at a temperature of from 1,200 to 1,600° C.to obtain the ceramic laminate 60, and then the first electrodes 28 areprinted and fired at predetermined positions on both surfaces of theceramic laminate 60. Subsequently, the piezoelectric/electrostrictivelayers 26 are printed and fired, and further, the second electrodes 30are printed and fired to form the piezoelectric/electrostrictiveelements 24 a and 24 b. After that, the terminals 32 and 34 are printedand fired in order to electrically connect the respective electrodes 28and 30 to the driving circuit.

In this process, when the materials are selected in such a manner thatthe firing temperature for each of the members is lowered in accordancewith the stacking sequence, for example, when platinum (Pt) is used forthe first electrode 28, lead zirconate titanate (PZT) is used for thepiezoelectric/electrostrictive layer 26, gold (Au) is used for thesecond electrode 30, and silver (Ag) is used for the terminals 32 and34, the material that has been already fired beforehand is not sinteredagain at a certain firing stage, and thus, it is possible to avoid theoccurrence of inconvenience such as peeling off and aggregation of theelectrode material or the like.

When appropriate materials are selected, it is also possible tosuccessively print the respective members of thepiezoelectric/electrostrictive elements 24 a and 24 b and the terminals32 and 34, followed by the firing at one time. Further, it is alsopossible to provide, for example, the respective electrodes 30 at a lowtemperature after forming the piezoelectric/electrostrictive layers 26.

It is also possible that the respective members of thepiezoelectric/electrostrictive elements 24 a and 24 b and the terminals32 and 34 are formed in accordance with the thin film formation methodsuch as the sputtering method and the vapor deposition method, and inthis case, it is not necessarily indispensable to perform the heattreatment.

In the formation of the piezoelectric/electrostrictive elements 24 a and24 b, it is preferably conducted that the piezoelectric/electrostrictiveelements 24 a and 24 b are previously formed on both surfaces of theceramic green laminate 58, i.e., on the respective surfaces of theceramic green sheets 52A and 52B, and then the ceramic green laminate 58and the piezoelectric/electrostrictive elements 24 a and 24 b areco-fired. Upon co-firing, it is possible that the ceramic green laminate58 and all the constitutional films of thepiezoelectric/electrostrictive elements 24 a and 24 b are subjected tofiring, or in alternative, those methods can be exemplified in that thefirst electrode 28 and the ceramic green laminate 58 are co-fired, andconstitutional films other than the second electrode 30 and the ceramicgreen laminate 58 are co-fired.

As a method of co-firing the piezoelectric/electrostrictive elements 24a and 24 b and the ceramic green laminate 58, such a method can beexemplified in that a precursor of the piezoelectric/electrostrictivelayer 26 is formed, for example, by the tape forming method using theslurry raw materials, and then the precursor of thepiezoelectric/electrostrictive layer 26 before firing is laminated onthe surface of the ceramic green laminate 58, for example, by heatpressure-securing, followed by conducting co-firing, so as tosimultaneously produce the movable section 20, the thin plate sections16 a and 16 b, the piezoelectric/electrostrictive layer 26 and thefixing section 22. In this method, however, it is necessary that theelectrode 28 be previously formed on the surface of the ceramic greenlaminate 58 and/or the piezoelectric/electrostrictive layer 26.

Other methods can be exemplified in that the electrodes 28 and 30 andthe piezoelectric/electrostrictive layer 26, which are theconstitutional layers of the piezoelectric/electrostrictive elements 24a and 24 b, are formed by screen printing on such parts of the ceramicgreen laminate 58 that finally become the thin plate sections 16 a and16 b, followed by co-firing.

The firing temperature of the piezoelectric/electrostrictive elements 24a and 24 b is appropriately determined by the materials constitutingthem, and is generally from 500 to 1,500° C., and preferably from 1,000to 1,400° C. for the piezoelectric/electrostrictive layer 26. In thiscase, in order to control the composition of thepiezoelectric/electrostrictive layer 26, it is preferable that thesintering is conducted in the presence of the evaporation source of thematerial of the piezoelectric/electrostrictive layer 26. In the casewhere the piezoelectric/electrostrictive layer 26 and the ceramic greenlaminate 58 are co-fired, it is necessary that the firing conditions ofthem agree with each other. The piezoelectric/electrostrictive elements24 a and 24 b are not necessarily formed on both surfaces of the ceramiclaminate 60 or the ceramic green laminate 58, but of course, may beformed only on one surface thereof.

Subsequently, unnecessary portions are cut off from the ceramic laminate60 formed with the piezoelectric/electrostrictive elements 24 a and 24 bas described above. The cutoff positions are located at side portions ofthe ceramic laminate 60, especially at portions, at which the hole 12based on the window 110 is formed on the side surfaces of the ceramiclaminate 60 by means of the cutoff (see cutting lines C1 and C2).

Those applicable as the cutoff method include the mechanical machiningsuch as the dicing machining, the slicing machining and the wire sawmachining, as well as the laser machining based on the use of, forexample, the YAG laser and the excimer laser, and the electron beammachining.

By the cutoff as shown in FIG. 18, the piezoelectric/electrostrictiveelements 24 a and 24 b are formed on the ceramic substrate 14C. Further,the cavity portion 102 is formed on the inner wall 20 a of the movablesection 20. Thus, the piezoelectric/electrostrictive device 10A isobtained where the stopper member 104 is formed on the fixing portion 22with its forward end 104 a entering into the cavity portion 102.

In this production method, when the unnecessary parts are cut off fromthe ceramic laminate 60, the piezoelectric/electrostrictive elements 24a and 24 b are formed on the ceramic substrate 14C. Further, when theunnecessary parts are cut off from the ceramic laminate 60, a cavityportion 102 is formed on the inner wall 20 a of the movable section 20in order to obtain a piezoelectric/electrostrictive device 10A in whicha stopper member 104 is formed in the fixing section 22 whose forwardend 104 a enters the cavity portion 102. Therefore, the productionprocess can be simplified, and the yield of thepiezoelectric/electrostrictive device 10A can be improved.

Especially, the unnecessary parts may be cut off from the ceramiclaminate 60 by means of machining, for example. In that case, somestress is applied and vibrates the thin plate sections 16 a and 16 b. Insome cases, the amplitude damages the thin plate sections 16 a and 16 b.However, according to this embodiment, the stopper member 104 isprovided. Therefore, the vibration (amplitude) during cut-off isrestricted, which can improve the productivity of thepiezoelectric/electrostrictive device 10A.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment and each of the modified examples 10Aa to 10Ai, the mechanism100 includes the cavity portion 102 formed on the inner wall 20 a of themovable section 20 and the stopper member 104 formed on the inner wall22 a of the fixing portion 22 whose forward end 104 a enters the cavityportion 102. Alternatively, as in the piezoelectric/electrostrictivedevice 10Aj according to a tenth modified example shown in FIG. 19, thecavity portion 102 may be formed on the inner wall 22 a of the fixingsection 22 and the stopper member 104 may be formed on the inner wall 20a of the movable section 20 in order to form the mechanism 100.

In this case, when the external force is applied to the movable section20 and the thin plate sections 16 a and 16 b, which causes the movablesection 20 and the thin plate sections 16 a and 16 b to vibrate to greatextent, the mechanism 100 can restrict the vibration (amplitude) of themovable section 20 and the thin plate sections 16 a and 16 b. As aresult, it can prevent the thin plate sections 16 a and 16 b from beingdamaged. In this case, the thin place sections 16 a and 16 b do not needto be thickened. Therefore, it does not deteriorate devicecharacteristics such as the displacement characteristic and the responsecharacteristic.

The piezoelectric/electrostrictive device 10B according to the secondembodiment will be described with reference to FIG. 20. The same symbolsare attached to those members that correspond to thepiezoelectric/electrostrictive device 10A and the respective modifiedexamples 10Aa to 10Ai, so as to omit the duplicate explanations.

As shown in FIG. 20, the piezoelectric/electrostrictive device 10Baccording to the second embodiment has the similar constitution as thepiezoelectric/electrostrictive device 10A according to the firstembodiment, except that the mechanism 100 for restricting amplitude ofthe thin plate sections 16 a and 16 b includes two buffer members 120 aand 120 b provided on the inner wall 22 a of the fixing section 22 and astopper member 122 provided on the inner wall 20 a of the movablesection 20 whose forward end 122 a enters between the two buffer members120 a and 120 b.

Also in this case, it is preferable that a shortest distance from theforward end 122 a of the stopper member 122 to the buffer member 120 aor 120 b in the direction in which the movable section 20 is displacedis not more than a tolerance limit of the amplitude of the movablesection 20 and the thin plate sections 16 a and 16 b.

In the piezoelectric/electrostrictive devices 10B according to thesecond embodiment, the forward end 122 a of the stopper member 122 hitsthe buffer member 120 a or 120 b so that the vibration (amplitude) ofthe movable section 20 and the thin plate sections 16 a and 16 b can berestricted. Especially, the appropriately adjusted aspect ratio ofheight and thickness of the buffer members 120 a and 120 b givesresilience so as to absorb shocks caused when the stopper member 122hits the buffer members 120 a and 120 b.

In this case, as in the piezoelectric/electrostrictive devices 10Baaccording to a modified example shown in FIG. 21, the two buffer members120 a and 120 b may be provided on the inner wall 20 a of the movablesection 20 and the stopper member 122 may be provided on the inner wall22 a of the fixing section 22.

The piezoelectric/electrostrictive device 10C according to the thirdembodiment will be described with reference to FIG. 22. The samereference numbers will be given to members corresponding to those in thepiezoelectric/electrostrictive devices 10A according to the firstembodiment and in each of modified examples 10Aa to 10Ai, and theirrepetitive descriptions will be omitted here.

As shown in FIG. 22, the piezoelectric/electrostrictive device 10C hassubstantially a similar constitution as thepiezoelectric/electrostrictive device 10A according to the firstembodiment, except that the mechanism 100 for restricting amplitude ofthe thin plate sections 16 a and 16 b includes a projecting portion 130formed from the inner wall 22 a of the fixing portion 22 into the hole12 and a shortest distance Li from the projecting portion 130 to thethin plate sections 16 a and 16 b is not more than a tolerance limit ofamplitude of the thin plate sections 16 a and 16 b.

Here the tolerance limit is an amplitude of the thin plate sections 16 aand 16 b when the stress applied to the joined portion between the thinplate sections 16 a and 16 b and the movable section 20 and the joinedpotion between the thin plate sections 16 a and 16 b and the fixingsection 22 is maximum (maximum value not to destroy).

In the piezoelectric/electrostrictive device 10C according to the thirdembodiment, the vibration (amplitude) of the movable section 20 and thethin plate sections 16 a and 16 b is not more than the tolerance limit.Thus, damages on the thin plate sections 16 a and 16 b can be preventedeffectively. Especially in this arrangement, vibration (amplitude)causing a damage on the thin plate sections 16 a and 16 b is restrictedeffectively when an external force is applied to the thin plate sections16 a and 16 b directly (and intensively), which is effective inpreventing the damage on the thin plate sections 16 a and 16 b.

While the example where the piezoelectric/electrostrictive elements 24 aand 24 b are formed on the pair of the thin plate sections 16 a and 16 bis described above, it is possible that thepiezoelectric/electrostrictive element 24 a is formed on one thin platesection 16 a as shown in the piezoelectric/electrostrictive device 10Daccording to the fourth embodiment in FIG. 23.

The piezoelectric/electrostrictive device 10D, in which thepiezoelectric/electrostrictive element 24 a is formed on only one thinplate section 16 a of the pair of mutually opposing thin plate sections16 a and 16 b as described above, makes it possible to decrease therigidity of the thin plate section 16 b on which thepiezoelectric/electrostrictive element 24 b is not formed.

As a result, when comparison may be made concerning the magnitude of thedisplacement obtained by operating one piezoelectric/electrostrictiveelement 24 a, between the piezoelectric/electrostrictive device (forexample, piezoelectric/electrostrictive device 10Ag as shown in FIG. 8),in which the piezoelectric/electrostrictive elements 24 a and 24 b areformed on both sides and the piezoelectric/electrostrictive device 10D,in which the piezoelectric/electrostrictive element 24 a is formed ononly one side, the piezoelectric/electrostrictive device 10D, in whichthe piezoelectric/electrostrictive element 24 a is formed on only oneside, has such a feature that it is possible to obtain greaterdisplacement owing to the effect that the rigidity of the thin platesection 16 b disposed on the opposed side is low.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment and each of the modified examples 10Aa to 10Ai, aplate-shaped member is provided as the stopper member 104. However,alternatively, as shown in the piezoelectric/electrostrictive device 10Eaccording to a fifth embodiment in FIG. 24, a step 140 may be provided.That is, the stopper member 104 in the piezoelectric/electrostrictivedevice 10E according to the fifth embodiment includes a combination ofthe stopper member 104 of the piezoelectric/electrostrictive device 10Aaccording to the first embodiment and the projecting portion 130 of thepiezoelectric/electrostrictive device 10C according to the thirdembodiment. In this arrangement, a thin portion 144 with smallerthickness in the X-axis direction is formed integrally into center of atop portion of a thick portion 142 with larger thickness in the X-axisdirection. A forward end 104 a of the thin portion 144 is arranged toenter the cavity portion 102 provided on the inner wall 20 a of themovable section 20. A shortest distance Li from the thick portion 142 tothe thin plate sections 16 a and 16 b and a shortest distance Lc fromthe forward end 104 a of the thin portion 144, which enters the cavityportion 102, to an inner wall 102 a of the cavity portion 102 in adirection in which the movable section 20 is displaced are set to notmore than the tolerance limit of the amplitude of the thin platesections 16 a and 16 b.

In this arrangement, the piezoelectric/electrostrictive device 10E getstotally stronger against the external force from its side surface(X-axis direction). Thus, it can further improve the shock resistanceagainst the external force applied to the movable section 20 and thethin plate sections 16 a and 16 b.

In the piezoelectric/electrostrictive device 10B according to the secondembodiment, thin plate-shaped members are provided as the buffer members120 a and 120 b, respectively. However, alternatively, as shown in thepiezoelectric/electrostrictive device 10F according to a sixthembodiment in FIG. 25, they can be thicker. A shortest distance Li fromthe respective buffer members 120 a and 120 b to the thin plate sections16 a and 16 b and a shortest distance Lc from the forward end 122 a ofthe stopper member 122 to respective buffer members 120 a and 120 b in adirection in which the movable section 20 is displaced may be set to notmore than the tolerance limit of the amplitude of the thin platesections 16 a and 16 b.

Also in this arrangement, the piezoelectric/electrostrictive device 10Fgets totally stronger against the external force from its side surface(X-axis direction). Thus, it can further improve the shock resistanceagainst the external force applied to the movable section 20 and thethin plate sections 16 a and 16 b.

The structure of the piezoelectric/electrostrictive device 10F accordingto the sixth embodiment can be applied to the 10th modified example(10Aj) of the piezoelectric/electrostrictive device 10A according to thefirst embodiment shown in FIG. 19 and the modified example (10Ba) of thepiezoelectric/electrostrictive device 10B according to the secondembodiment shown in FIG. 21.

As shown in FIGS. 19 and 21, when the movable section 20 is providedwith the stopper member 104 or the buffer members 120 a and 120 b, theweight of the movable section 20 increases. As a result, its responseperformance is reduced to some extent if it is used as an actuator.However, it is effective for improving the detection sensitivity when itis used as a sensor using inertial weight like an acceleration sensor.

The piezoelectric/electrostrictive device described above can beutilized as the active device including, for example, vibrators,resonators, oscillators, and discriminators for the communication andthe power generation, various transducers, various actuators, frequencyregion functional parts (filters), transformers, as well as the sensorelement for various sensors including, for example, ultrasonic sensors,acceleration sensors, angular velocity sensors, shock sensors and masssensors. Especially, The piezoelectric/electrostrictive device can bepreferably utilized for various actuators to be used for the mechanismfor adjusting the displacement and the positioning and for adjusting theangle for various precision parts such as those of optical instrumentsand precision mechanical equipment.

It is a matter of course that the piezoelectric/electrostrictive deviceand the method of producing the same according to the invention are notlimited to the embodiments described above, which may be embodied inother various forms without deviating from the gist or essentialcharacteristics of the invention.

What is claimed is:
 1. A piezoelectric/electrostrictive device having apair of mutually opposing thin plate sections, a movable section, and afixing section for supporting said thin plate sections and said movablesection, said piezoelectric/electrostrictive device comprising: one ormore piezoelectric/electrostrictive elements arranged on at least onethin plate section of said pair of thin plate sections; and a holeformed by both inner walls of said pair of thin plate sections, an innerwall of said movable section, and an inner wall of said fixing section,wherein a mechanism is provided for restricting amplitude of said thinplate sections.
 2. A piezoelectric/electrostrictive device according toclaim 1, said mechanism comprising: a cavity portion formed in saidinner wall of said movable section; and a stopper member provided onsaid inner wall of said fixing section, said stopper member having atleast one forward end portion extending into said cavity portion.
 3. Apiezoelectric/electrostrictive device according to claim 2, wherein ashortest distance from said forward end of said stopper member to aninner wall of said cavity portion in a direction of displacing saidmovable section is not more than a tolerance limit of amplitude of saidthin plate sections.
 4. A piezoelectric/electrostrictive deviceaccording to claim 1, said mechanism comprising: a cavity portion formedin said inner wall of said fixing section; and a stopper member providedon said inner wall of said movable section, said stopper member havingat least one forward end portion extending into said cavity portion. 5.A piezoelectric/electrostrictive device according to claim 4, wherein ashortest distance from said forward end of said stopper member to aninner wall of said cavity portion in a direction of displacing saidmovable section is not more than a tolerance limit of amplitude of saidthin plate sections.
 6. A piezoelectric/electrostrictive deviceaccording to claim 1, said mechanism comprising: at least two buffermembers formed on said inner wall of said fixing section; and a stoppermember provided on said inner wall of said movable section, said stoppermember having at least one forward end portion extending between said atleast two buffer members.
 7. A piezoelectric/electrostrictive deviceaccording to claim 6, wherein: a shortest distance from said forward endof said stopper member to said buffer members in a direction ofdisplacing said movable section is not more than a tolerance limit ofamplitude of said thin plate sections.
 8. Apiezoelectric/electrostrictive device according to claim 1, saidmechanism comprising: at least two buffer members formed on said innerwall of said movable section; and a stopper member provided on saidinner wall of said fixing section, said stopper member having at leastone forward end portion extending between said at least two buffermembers.
 9. A piezoelectric/electrostrictive device according to claim8, wherein: a shortest distance from said forward end of said stoppermember to said buffer members in a direction of displacing said movablesection is not more than a tolerance limit of amplitude of said thinplate sections.
 10. A piezoelectric/electrostrictive device according toclaim 1, said mechanism comprising: a projecting portion formed fromsaid inner wall of said fixing portion into said hole, wherein: ashortest distance from said projecting portion to said thin platesections is not more than a tolerance limit of amplitude of said thinplate sections.
 11. A piezoelectric/electrostrictive device according toclaim 1, wherein said thin plate sections, said movable section, saidfixing section and said mechanism comprise an integrated ceramicsubstrate formed by simultaneously firing a ceramic green laminate,followed by cutting off unnecessary portions.
 12. Apiezoelectric/electrostrictive device according to claim 11, whereinsaid piezoelectric/electrostrictive elements are of a film form andintegrated with said ceramic substrate by firing.
 13. Apiezoelectric/electrostrictive device according to claim 1, wherein saidpiezoelectric/electrostrictive elements have apiezoelectric/electrostrictive layer and a pair of electrodes formed onsaid piezoelectric/electrostrictive layer.
 14. Apiezoelectric/electrostrictive device according to claim 13, whereinsaid piezoelectric/electrostrictive elements are constituted bylaminating a plurality of said piezoelectric/electrostrictive layers andsaid pair of electrodes.
 15. The piezoelectric/electrostrictive deviceaccording to claim 1, wherein said hole is filled with a gel-likematerial.